1. Technical Field
The present disclosure relates to lithium iron phosphates, methods for making the same, and rechargeable lithium ion batteries using the same. The present disclosure particularly relates to a lithium iron phosphate hierarchical structure, a method for making the same, and a rechargeable lithium ion battery using the same.
2. Description of Related Art
Olivine type lithium iron phosphate (e.g. LiFePO4), is an attractive cathode active material. Lithium iron phosphate has advantages of high safety, low cost, and environmental friendliness. However, lithium iron phosphate has deficiencies such as a low electronic conductivity and a slow diffusion of lithium ions. Efforts on improving the electronic conductivity of lithium iron phosphate have been made by carbon coating the lithium iron phosphate particle surface, and doping the lithium iron phosphate with metal ions. In the aspect of improving the diffusion of lithium ions, particle size minimization of the lithium iron phosphate has been undertaken to decrease a diffusion path of the lithium ions. Hydrothermal method and solvothermal method are two common methods for preparing nano sized lithium iron phosphate.
However, disadvantages will occur when the particle of the lithium iron phosphate is nano in size. For example, a tap density of the nano sized particles is lower than micron sized particles. The smaller the particle size of the lithium iron phosphate, the more binder and conductive agent will be required during the preparing of the cathode electrode of the lithium ion battery. The increased content of the binder and conductive agent will decrease a capacity per volume of the lithium ion battery. Furthermore, the nano-sized particles have a large specific surface area, and are difficult to process during the preparation of an electrode slurry and coating the electrode slurry on a cathode current collector to form a uniform cathode electrode.
What is needed, therefore, is to provide a lithium iron phosphate hierarchical structure which can avoid the above described disadvantages of the nano sized lithium iron phosphate particles. A relatively simple method for making the same, and a lithium ion battery using the same are also provided.